Models hold a Samsung "Galaxy S3" and the "Galaxy S3 mini' (R) phones in Frankfurt in this October 11, 2012 file photo. Samsung Electronics' Galaxy S3 became the world's best-selling smartphone model last quarter, pushing aside Apple Inc's iPhone, which has dominated the chart for more than two years, research firm Strategy Analytics said on November 8, 2012. REUTERS/Ralph Orlowski/Files

BOSTON -- A research firm says that Samsung's Galaxy S3 overtook Apple's (AAPL) iPhone 4S as the world's best-selling smartphone for the first time in the third quarter.

Boston-based Strategy Analytics said Thursday that the S3 shipped 18 million units in the third quarter of this year. Apple's iPhone 4S, meanwhile, shipped 16.2 million units, as many people likely held off to buy its successor. Apple launched the iPhone 5 on Sept. 21.

Strategy Analytics' executive director, Neil Mawston, says the Galaxy's top position is likely to be short-lived. The iPhone 5 sold an estimated 6 million units in the third quarter, which ended on Sept. 30.

Apple shares continued their recent decline in morning trading, falling $8.62, less than 2 percent, to $549.38. The stock was over $700 two months ago.